1. Field of the Invention
The present invention relates generally to treatments of vascular disease and, more particularly, to systems and methods for delivering stents to a bifurcated vessel.
2. Description of the State of the Art
The use of medical devices for treating medical conditions in patients is well known. In particular, medical devices are commonly used during the treatment of vascular conditions involving lesions that block or restrict blood flow within body vessels. These procedures usually require that the medical devices be delivered to the treatment site by accessing and tracking through the vessel system.
For example, in a medical procedure known as percutaneous transluminal coronary angioplasty (PTCA), a balloon catheter is used to treat a coronary artery (or other vessel), which has become narrowed or restricted due to the accumulation of plaque along the artery wall. In the PTCA procedure, a balloon catheter is inserted percutaneously and is advanced through the lumen of the coronary artery to the site of a stenosis or blockage. The balloon is then inflated to press the plaque against the artery wall thereby dilating the lumen of the artery and establishing adequate blood flow.
After the PTCA procedure has been performed, a stent may be deployed to prevent restenosis at the treatment site and maintain a clear pathway for the flow of blood. A balloon catheter with an expandable stent mounted over the balloon is advanced through the lumen until the stent is in the desired location. The balloon is then temporarily inflated, thereby expanding and implanting the stent in the vessel. The balloon is then deflated and the balloon catheter assembly is removed from the lumen, leaving the expanded and implanted stent in the vessel to support the vessel wall and prevent development of restenosis.
Although most diseased arteries can be successfully treated in this manner using conventional balloon catheters and stents, arteries that are diseased at a bifurcation are difficult to treat with the devices currently available. For example, when a conventional balloon catheter is used to treat one of the vessel passages at a bifurcation during PTCA, the pressure from the expansion of the balloon in the treated passage can restrict the flow of blood to the untreated passage by pushing the carina over the ostium of the untreated vessel. In addition, the pressure of the balloon in the treated passage may shift the plaque from the treated passage to the untreated passage. If sufficient plaque is shifted to the untreated passage, the ostium of the untreated passage can become so occluded that it becomes difficult or impossible to insert a guidewire and catheter to perform a PTCA in the untreated vessel.
Effectively deploying a stent at a bifurcation is also very challenging. Conventional stents are designed to repair areas of blood vessels that are removed from bifurcations and, since a conventional stent generally terminates at right angles to its longitudinal axis, the use of conventional stents in the region of a vessel bifurcation may result in blocking blood flow of a side branch (commonly referred to as “jailing” the side branch) or fail to repair the bifurcation to the fullest extent necessary. To be effective, the stent must overlay the entire circumference of the ostium to a diseased portion and extend to a point within and beyond the diseased portion. Where the stent does not overlay the entire circumference of the ostium to the diseased portion, the stent fails to completely repair the bifurcated vessel. In this case, the stent also acts as a barrier to passing a secondary balloon catheter or stent delivery system, thereby further complicating and increasing the risk of a failed procedure.
To overcome the problems and limitations associated with the use of conventional stents, a Y-shaped stent has been proposed for the treatment of bifurcations. Such a stent has the advantage of completely repairing the vessel at the bifurcation without obstructing blood flow in the other portions of the bifurcation. In addition, such a stent allows access to all portions of the bifurcated vessel should further interventional treatment be necessary. In a situation involving disease in the origin of an angulated aorta-ostial vessel, such a stent would have the advantage of completely repairing the vessel origin without protruding into the aorta or complicating repeat access. The proposed Y-shaped stent provides an improved device for repairing bifurcations. However, the delivery and deployment of such a stent cannot be easily accomplished with a conventional balloon catheter.
Because a conventional balloon catheter is not adequate for treating an arterial bifurcation, many physicians currently employ a “kissing balloon” technique in which two separate balloon catheters are inserted into a guide catheter and each balloon tracks over a separate guidewire. The guide catheter is advanced to a point proximal to the bifurcation site and two guidewires are then advanced from the distal end of the guide catheter into separate vessel passages. The two balloon catheters then track over the guidewires into the respective passages. The balloons are simultaneously inflated using either separate inflation media or from a single source using a manifold which divides the flow. The two catheters are used together for PTCA or stenting so that both vessel passages at a bifurcation site can be treated simultaneously.
Although generally effective, the use of two single balloon catheters to treat arterial bifurcations has significant drawbacks. For example, the presence of two similar catheters exiting the proximal end of the guide catheter makes it difficult for a physician to manage both devices without becoming confused as to which catheter controls a particular balloon. Furthermore, the presence of two balloon catheters within one guide catheter creates a large device profile thereby limiting the amount of radiopaque dye, which can be injected into the vessel to allow the physician to view the bifurcation. Additionally, the profile of the combined balloon catheters may require the physician to use a larger guide catheter than preferred. Further still, a system with two separate balloon catheters has increased stiffness in the proximal system region, resulting in deliverability difficulties.
Many of the existing concepts for bifurcation stent delivery systems include a single catheter shaft that branches into separate catheter shaft branches having associated balloons. The aim of these systems is to overcome the drawbacks of using two separate balloon catheters, as previously discussed. While reasonably effective, these systems also include drawbacks of their own. For example, these systems generally must track over two guidewires that are initially placed within the branches of the bifurcated vessel. Since each guidewire is potentially twisted around the other, there may be significant resistance to deliverability of the catheter system to the disease location. Additionally, since the proximal catheter body is usually attached to the distal catheter branches through the use of a connection of some nature, the stiffness and profile of the system is increased at the connection locale. This can cause further difficulties in tracking to the disease location as mentioned earlier.
Efforts have been made to develop a balloon catheter that is designed specifically for the treatment of arterial bifurcation. Such efforts have led to the proposal of a Y-shaped balloon disposed at the distal end of a catheter that is inflated in a bifurcation to treat both passages simultaneously. Although a Y-shaped balloon would provide an improvement over the use of two separate balloon catheters, the proposed device may not be practical due to challenges of manufacturing a Y-shaped balloon, attaching it to a catheter shaft, and properly positioning it at a bifurcated blood vessel.
The present invention provides a stent delivery system for the treatment of bifurcated vessel disease that seeks to overcome the downfalls of the prior art. This is achieved by the advantageous aspects of the invention. For example, as a result of the system design, a stent can be deployed at a bifurcation in a way that provides complete coverage of the ostium circumference. Deliverability of the stent to the bifurcation is also improved, since the system incorporates features to reduce profile and improve system flexibility. Further still, at least one embodiment of the system provides the advantage of delivering the system to the bifurcation over a single guidewire, thereby reducing the risk of encountering guidewire wrapping that hinders stent deliverability.